This invention relates to medical electrical stimulation electrodes in general and to implantable defibrillation electrodes in particular.
It is well known that cardiac arrhythmias may be controlled with devices such as implantable defibrillators. Past electrodes which deliver defibrillation therapy have been constructed of metal mesh adhered to a silicone rubber backing as disclosed in Heilman et al. in U.S. Pat. No. 4,291,707 or have been constructed of metal electrode coils adhesively bonded to a silicone rubber backing as disclosed in Holleman et al. in U.S. Pat. No. 4,971,070.
These electrodes have been manufactured using various techniques. In the case of the Heilman electrode, the electrode metal meth is either sandwiched between two layers of silicone rubber sheeting, one solid, and the other with open windows to allow for current distribution. In another embodiment of this electrode construction, the metal mesh is stitched onto the rubber sheeting. The problem with this manufacturing process is that the electrode is not firmly attached to the silicone rubber sheeting in all areas. Thus, tissue will have a tendency to grow into the electrode mesh and separate the electrode from the backing. If the need arises for explanting the electrode, complications arise due to the difficulty in separating the electrode from the ingrown tissue. In addition, the manufacturing methods are somewhat cumbersome to utilize.
In the case of the Holleman electrode, the electrode coils are adhesively bonded to the silicone sheeting either with or without a central silicone core being inserted into the coil. This technique involves an adhesive bonding step which must be carefully administered in order to ensure adequate bonding to all the surfaces. In addition, by using an adhesive, another material, which must be biocompatible, is added to the device tubs complicating matters.
It would be advantageous to have a process that would allow simple assembly and good control over the amount of exposed electrode and the amount of electrode adhesion to the insulative backing. This can be accomplished by completely embedding the electrode material in silicone or other elastomer, utilizing a molding operation. Then the electrode can be exposed via a material removal process. The problem with many material removal processes is that they are not easily controllable. If one were to try to machine, grind, or cut the electrode, there would be a high probability that the electrode material would be damaged in the process. In addition, rubber is a resilient material that is not readily amenable to some of the mentioned processes